We have to fill cities 1, 4 and 5 with at least one institution, since we know that cities 2, 3, and 6 all have at least one in them already.
Well, what do we have left? We have three H's and one J. We know that, according to the rules, wherever a J goes, one of the H's will also be there. So one of the three remaining cities will have a J and an H and the other two will have an H each.
So what is the common factor here? The H.
Cities 1, 4 and 5 MUST each have an H, and the J COULD be in either city 1, 4, or 5. Since this is a must be true question, answer choice (D) is our answer because city 4 MUST have an H in it, whereas city 4 COULD have a J in it, but it doesn't have to.
So answer choice (E) doesn't HAVE TO be true, but answer choice (D) MUST BE TRUE.
Hope that clears things up! Please let us know if you have any other questions.
